Earlier quoted context omitted.
I have wondered about this, but even if botulinum or listeria are present, won't they grow very slowly in the refrigerator? I would think that defrosting for 12 hours or so at refrigerator temperatures would still be fairly safe. Or is the quantity that can be dangerous so minute that it doesn't matter?
Perhaps its one of those things where “95% of the time you’ll be fine, but be careful if you do it 20 times, because botulism only needs to happen once.”
Probably just a locution, but be careful with that idea about numbers:
The probability of remaining in a safe zone of 95% for 20 consecutive times is ~36%. It ( (1-(1/n))^n ) approximates to 1/e.
The number of tries to reduce that 95% to a 50% coin toss is 13. It is not fully intuitive. One will put his threshold wherever one may think appropriate, but. A chance of tenth, a hundredth, a thousandth etc. for ten, a hundred, thousand etc. times approximates to 63.2%.
...Maybe a locution like 'Maybe 9 out of 10 times you'll be fine, but be careful about doing it 7 times' could work well (as 6.931 approximates the risk to a coin toss).